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TREE   PORCUPINES

in both families we have long-tailed and short-tailed forms.
Cercolabes corresponds to Atherura or Tricky s, and JZrethizon
to Hystrix.

The genus ISretliizon, the " Urson" of Canada, has a short,
stumpy tail Its spines are almost hidden by enveloping hair.
The fore-feet have four, the hind-feet five toes. The short tail of
this creature is remarkable when we reflect upon its climbing
habits. It appears, however, to be a weapon with which it
strikes sideways at the enemy.

Of the Itfeotropical genus Cercolabes (sometimes called Sphin-
gurus, Synetheres, or Coendou) there are some eight or nine
species, all found in Central ^nd South Ame.rica. The animal is

ITiG. 244.óBrazilian Tree Porcupine.     Sphingwrus jprehensiUs.     x£.
arboreal, and has in correspondence with that habit a prehensile
tail. The spines are not so stout as in the Ground Porcupines,
and are often coloured yellowish or reddish. In correlation with
its tree-frequenting habits the bones of Cercolabes show certain
differences from those of the Ground Porcupines. The scapula is
broader and rounder in front than is that of Hystrix; the
phalanges of the thumb (which is rudimentary) are fused
together as in the Canadian JZrethizon ; but those of the very
small hallux are also fused, whereas in JSrethizon, as in Hystrix,
they are separate. Tn one species, C, insidiosus, Sir W. ITlower
states that there are as many as seventeen dorsal vertebrae
and thirty-six caudals. The tail is thus very long. In O.
there are fifteen dorsals and twenty-seven caudals; eight
reach the sternum, which is composed of seven pieces, the